ALBANY — A top county official from New York City’s northern suburbs announced Wednesday that he will run for governor, launching an uphill fight to unseat heavily favored incumbent Democratic Gov. Andrew Cuomo.

The video announcement makes official what has become increasing apparent this year as the Republican, Westchester County Executive Rob Astorino, crisscrossed the state and lobbed criticisms at the governor on the state’s taxes, business climate and sluggish population growth.

“I’m tired of listening to the fairy tale that everything is just great when it’s just the opposite. I’m tired of watching New York’s decline,” Astorino said in the video posted on his campaign website.

New York Republicans will hold their nominating convention in May. Celebrity businessman Donald Trump has said he would consider a run if the state party unifies behind him. A Trump spokesman said Wednesday that Astorino’s announcement does not change that.

Though Astorino easily won a second term last November, the former radio executive is little known beyond his suburban stronghold of Westchester, north of New York City, and faces daunting odds if he becomes the Republican nominee. There are twice as many Democrats in New York state than Republicans, and polls have shown Cuomo with commanding leads over potential GOP candidates. A Siena College poll released last week found Cuomo, a possible 2016 presidential candidate, leading Astorino by 42 points and Trump by 44 points.

That same poll found 73 percent of respondents either didn’t know Astorino or had no opinion about him.

“Goliath, meet David,” state GOP chairman Ed Cox said in a statement.

Astorino points out that he is a Republican who has won twice as head of the executive branch in a Democratic county, the first time in 2009 as a relative unknown.

Still, the lack of name recognition could make Astorino particularly vulnerable against Cuomo, who reported $33 million this year in available campaign cash. Astorino, who reported $1 million on hand, has said he is confident he could raise enough money to win.

“We look forward to an entertaining Republican primary process and are ready to run against whomever their nominee is in September,” said state Democratic Committee spokesman Peter Kauffmann.